The path of cancer progression is determined by alterations in the regulatory mechanisms of growth/invasion and differentiation. The expression of Id-1 protein (an inhibitor of basic helix-loop-helix transcription factors) has been reported to be dysregulated in over twenty types of cancer, and suggested as a key determinant of tumorigenesis and/or metastasis in a wide range of tissues, particularly in the breast. Our studies on Id-1 expression in normal and cancerous breast cells, in mouse mammary glands as well as in human breast cancer biopsies, demonstrated that Id-1 gene expression was associated with a proliferative, migratory and invasive phenotype. Reducing Id-1 expression could therefore provide a rational therapeutic strategy for the treatment of aggressive breast cancer. We recently showed that CBD, a non-psychoactive cannabinoid compound derived from cannabis, could represent the first non-toxic exogenous agent that can down-regulate Id-1 expression. This down-regulation, and the corresponding inhibition of human breast cancer cell proliferation and invasiveness, could provide a potential mechanism for the anti-metastatic activity of the compound. The aims of this proposal are to determine 1) the extent to which novel CBD analogs reduce breast cancer cell proliferation, invasion and metastatic progression in mice through Id-1 down-regulation, and 2) the mechanisms behind the inhibition of Id-1 expression by cannabinoid compounds. The proposed experiments have the potential to lead to the development of novel compounds for the treatment of breast cancer metastasis. Additionally, the information gained from the outlined experiments will greatly broaden our knowledge of both Id-1 and cannabinoid biology as it pertains to cancer progression. Understanding these molecular events may also lead to the future development of novel, efficacious and non-toxic treatments for breast cancer patients. PUBLIC HEALTH RELEVANCE: We hypothesize that cannabinoids, well-tolerated compounds that are already being used in clinical trials for purposes unrelated to their anticancer activity, will be of benefit for patients with breast cancers through their ability to down-regulate Id-1 expression and corresponding breast cancer cell invasion and metastasis. Using mouse models that can mimic the role of Id-1 protein during tumor progression in humans, we expect to develop novel strategies to specifically target its expression for therapeutic purposes. This research could lead to new areas of investigation in the treatment of aggressive forms of breast cancer, which spread to other parts of the body, with novel cannabinoid compounds such as analogs of cannabidiol.